The translational dynamics of specific cell membrane components will be studied, with particular emphasis placed on the systematic transport processes associated with active cell locomotion. A variety of modern optical methods will be used, principally the recently developed fluorescence photobleaching recovery. In this technique, transport rates are determined by monitoring the recovery of fluorescence in a small region of the cell surface initially photobleached irreversibly by an intense focused laser light pulse. Membrane flow and counterflow will be characterized for a variety of cell types with a variety of fluorescent probes and membrane ligands. The role of cytoplasmic structures - microtubules and microfilaments -will be investigated with the use of drugs such as colchicine and cytochalasin B. This approach will be extended finally, to study, on the molecular level, the class of intercellular interactions termed contact inhibition of locomotion. It is thereby hoped that important mechanistic differences in structural dynamics and intercellular communication can be elucidated between normal and neoplastic cells.